Introduction
Moonstone is a feldspar group known for its blue sheen, also referred to as adularescence. It is composed of two feldspar minerals: orthoclase and albite. The reason moonstone exhibits moon-like glow is due to the intergrowth of these two minerals. As the mineral cools, orthoclase and albite separate into alternating layers. When lights enter the gemstone and travel through these layers, it reflected and refracted, creating the characteristic blue-white sheen, or sometimes even other colors, seen from specific angles when the stone is cut and polished.
(Figure 1) 1
Moonstone
- Crystal system: monoclinic crystal system
- Hardness: 5
- Specific gravity: 2.57
- Luster: vitreous luster
- Transparency: transparent to translucent
- Color: colorless, gray, white, orange red
- Index of refraction: 1.52~1.53
- Birefringence: 0.006
- Fluorescence: pink fluorescence at short wave
- Cleavage: complete cleavage
- Properties：blue sheen, developed cleavage
- Imitation: glass
The commercial value of Moonstone
Ornamental
The classic blue sheen of moonstone is quite rare in natural gemstones and can generally be distinguished from other natural gemstones with naked eyes. Among artificial imitations, there’s a type called opalite glass, which use man-made glass with emulsion to create a blue-white luster. Though it looks similar, it often contains visible bubbles. Under magnifier, some moonstone exhibit “centipede-like inclusions”, which are formed by the cleavage plane of the feldspar. These inclusions are highly distinctive characteristic for identification.
Moonstone is a renowned phenomenon gemstone. In addition to the basic 4Cs(carat, color, clarity, cut), the optical effect is a crucial consideration. High-quality moonstone is semi-transparent, while lower quality ones appear milky and turbid with less adularescence. The best moonstone display a vivid blue sheen when viewed from the front; if this effect is only seen in parts, the gemstone’s value decreases. Moreover, moonstones exhibiting both cat’s eye effect and blue sheen are extremely rare and valuable!
Moonstone has a relatively high hardness but has developed cleavage, so should be careful of collisions in order to avoid the gemstone to break along its cleavage plane.
Most commercially available moonstones are orthoclase, although occasionally plagioclase feldspar can also be found. However, plagioclase feldspar is only considered as moonstone if it exhibits the characteristic “blue sheen”.
Other feldspar groups:
A gems with unique optical effects – Labradorite
A sparkling gemstone – Sunstone
A gemstone with mysterious river-colored — Amazonite
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